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Many kinds of bacteria exist in plants and soil. Some infect plants with diseases while others seemingly have no effect at all, but a special group of bacteria bonds with annual garden peas (Pisum sativum) in a mutually beneficial relationship that benefits a pea harvest and garden. The symbiosis between bacteria and peas happens through a process known as nitrogen fixation. The beneficial bacteria convert atmospheric nitrogen into plant-nourishing nitrogen that peas can use.

Nitrogen and Peas

Plants need larger amounts of nitrogen than any other essential plant nutrient. Nearly 80 percent of air is nitrogen gas, but that is not a form that plants can use. Instead, peas and other plants naturally rely on soil-borne nitrogen to meet their needs. Because plants use so much nitrogen and the element moves through soil quickly, plants often suffer nitrogen deficiencies unless the nutrient is replenished. Fertilizer is the only path to replacement nitrogen for most plants in depleted soil, but peas are different. As with all members of the legume family (Fabaceae), the relationship between peas and specific bacteria can make nitrogen fertilizer unnecessary.

Nitrogen Fixation

The natural conversion of atmospheric nitrogen into plant-usable nitrogen falls to bacteria. This process of nitrogen fixation happens in peas when specific bacteria take up residence in pea roots. Inside bumpy root protrusions known as nodules, bacteria convert nitrogen gas into ammonia nitrogen. Chemists mimic that process when producing chemical fertilizers, such as ammonium nitrate. After nitrogen becomes fixed within the root nodules, peas can use that nitrogen to fuel their growth. In turn, pea plants provide the carbohydrates bacteria need for energy to do the work. The bacterial boost in nitrogen yields improvements in pea nutrition, growth and productivity.

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Pea Inoculant

Nitrogen fixation happens naturally when existing soil bacteria enter pea roots. Unless you've grown peas in your garden before, nitrogen-fixing bacteria may be absent. Bacteria left from other legume crops may not help peas. Treat pea seeds with a commercially available inoculant to get the proper bacteria out in force. The nitrogen-fixing bacteria Rhizobium leguminosarum bonds with peas. Mix the inoculant with cool, non-chlorinated water to make a mudlike pea seed coating. One product recommends mixing 8 1/2 ounces of water with 2 1/2 ounces of inoculant and 50 pounds of seeds. Let the coated pea seeds dry one to three minutes, and then plant them immediately.

Other Considerations

Bacteria in soil and inoculants are living organisms, sensitive to light, heat and other forces. Common seed fungicides may kill these beneficial bacteria. Anything that inhibits plant health or growth also limits nitrogen fixation. When problems such as drought, cold temperatures, disease or nutrient deficiencies stress peas, the plants limit the bacteria's share of carbohydrates. Undernourished bacteria slow down or stop fixating nitrogen. These beneficial bacteria build up over time, but peas use most of the nitrogen produced each season as it is made. Your garden will benefit when pea plants are tilled into the soil or decompose at the growing season's end.

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About the Author

Jolene Hansen is a lifelong gardening enthusiast and former horticulture professional. She is passionate about reshaping the way people experience gardens and gardening. Hansen's work appears regularly in consumer and trade publications, as well as numerous internet gardening and lifestyle channels.